12 TECHNICAL BULLETIN 149, U. S. DEPT. OF AGBICULTTJRE 



To determine this point preliminary experiments were conducted 

 in the writer's apiary at Bronson, Mich., during the spring of 1924. 

 A search was made of the entire apiary, and the combs showing the 

 best growth of mycelium and spores of Penicillia and Aspergilli 

 were selected. Both brood combs and extracting combs were found 

 to contain these forms. Brood combs overgrown with Penicillia 

 were readily found in colonies that had wintered badly or had died 

 during the winter. Combs even partially covered with Aspergilli 

 were less abundant. In order to find a sufficient number of combs 

 containing Aspergilli, it was necessary to examine not only the brood 

 combs but the extracting combs as well. 



The combs containing the fungi to be tested for pathogenicity 

 were placed in weak, but apparently healthy, colonies. As a result 

 of these inoculations a varying degree of loss of bees was noticeable, 

 and in one case the death of the entire colony resulted. The in- 

 fected bees appeared to die at a considerable distance from their 

 hives, and dead bees were not found in unusual numbers on the bot- 

 tom board or near the hives. Numerous bees unable to fly were 

 found crawling about the apiary during the time the inoculation 

 experiments were in progress. It was found that about 50 per cent 

 of the dead bees collected from the fronts of the colonies that had 

 been given infected combs prQ,duced conidiophores of apparently 

 the same species as those used in the inoculations. In order to pro- 

 mote the production of conidia -the dead bees were kept in moist 

 chambers at room temperature for from 5 to 7 days. 



The results obtained in these preliminary experiments were con- 

 sidered sufiicient to warrant further study. The experiments which 

 follow were therefore made with pure cultures of a considerable 

 number of fungi suspected of possessing qualities pathogenic to bees. 



INOCULATION EXPERIMENTS WITH PURE CULTURES 



Experiments with pure cultures of the organisms were of two 

 general types. In the one, adult bees were inoculated and kept in 

 cages during the experiment. In the other, large quantities of the 

 inoculum were used on bees in normal colonies. 



EXPERIMENTS WITH CAGED BEES 



The types of cages used for confining the bees during the experi- 

 ments are shown in Plate 1, A and B. The cage shown in A was 

 found to be the most convenient, as the removal of individual bees 

 was facilitated. In this cage, also, the food supply was easily reached 

 by the bees. 



Some trouble was experienced at first in devising a method of 

 feeding that would furnish the bees an abundant supply of food at 

 all times without danger of daubing them with it. This smearing 

 invariably happened in the use of candy in culture dishes when the 

 nutrient agar was not thoroughly dried, since water was rapidly 

 taken up from the agar by the candy. 



A satisfactory method was finally found and used in the succeed- 

 ing experiments. Small vials were filled with sugar solution or 

 honey and covered with one or more thicknesses of cheesecloth fas- 

 tened with rubber bands. These were inverted on the screen covers 



